Apparatus and method for diagnostic gas analysis

Abstract

A handheld, small but accurate and reliable device for diagnostic NO measurements using a NO sensor, where the parameters governing the taking of the sample are different from the parameters optimal for the accuracy of said NO sensor I described. By temporarily storing a portion of the exhaled air, and feeding this to the sensor at a flow rate adapted to the NO sensor, the accuracy and sensitivity of a system/method involving NO sensors, in particular electrochemical NO sensors, can be increased. The method for diagnostic NO measurements comprises steps for controlling the inhalation of NO free air, as well as the exhalation, both by built-in means and by audible and/or visual feedback to the patient.

1. A device for diagnostic NO measurements, the device comprising:
 a combined inlet and outlet configured to provide NO-scrubbed inhalation air to a patient and to accept an exhalation air at an exhalation flow rate; 
 a NO scrubber connected to the combined inlet and outlet along an inhalation flow path, the NO scrubber configured to provide NO-scrubbed air to the combined inlet and outlet; 
 a buffer chamber connected to the combined inlet and outlet along an exhalation flow path, the buffer chamber configured to temporarily hold a sample of the exhalation air for a period of time; 
 a flow regulator positioned between the combined inlet and outlet and the buffer chamber, the flow regulator configured to control the exhalation flow rate to 20-800 ml/s; 
 an electrochemical NO sensor connected to the buffer chamber, the electrochemical sensor configured to receive the sample of exhalation air temporarily held by the buffer chamber; and 
 means for feeding the temporarily held sample of the exhalation air from the buffer chamber to the electrochemical NO sensor at a suitable flow rate for the electrochemical NO sensor, wherein the suitable flow rate for the electrochemical NO sensor is lower than the exhalation flow rate. 
 
     
     
       2. The device according to  claim 1 , wherein the suitable flow rate for the electrochemical NO sensor is about 0.5to 15 ml/s. 
     
     
       3. The device according to  claim 1 , wherein the device comprises means for equalizing the humidity of the sample. 
     
     
       4. The device according to  claim 3 , wherein said means for equalizing the humidity of the sample comprises a length of tube, made from a catalytic membrane material. 
     
     
       5. The device according to  claim 1 , wherein the device further comprises control electronics for verifying the parameters of the inhalation and controlling the parameters of exhalation. 
     
     
       6. The device according to  claim 5 , wherein said control electronics comprise a pressure sensor and means for giving feedback to the patient. 
     
     
       7. The device according to  claim 5 , wherein said control electronics further comprise a flow sensor and means for controlling the flow and/or giving feedback to the patient. 
     
     
       8. The device according to  claim 5 , wherein said control electronics further comprise a pressure sensor capable of measuring absolute pressure in order to make it possible to compensate for varying partial pressure of NO depending on variations in ambient pressure. 
     
     
       9. The device according to  claim 1 , wherein the buffer chamber comprises a cylinder with a movable piston. 
     
     
       10. The device according to  claim 1 , wherein the buffer chamber comprises a length of tube. 
     
     
       11. A method for diagnostic NO measurements, the method comprising the steps of:
 a patient inhales through an inhalation flow path of a device comprising a flow regulator, an electrochemical NO sensor, a NO scrubber, and a buffer chamber, 
 said patient exhales air into an exhalation flow path of said device, wherein an exhalation flow rate and pressure is controlled to a preset value between 20-800 ml/s by the flow regulator, 
 a sample of the exhaled air from said patient is temporarily held for a period of time in said buffer chamber, 
 said sample is fed to said electrochemical NO sensor at a flow rate lower than the exhalation flow rate, and 
 an NO concentration is determined in said sample. 
 
     
     
       12. A method according to  claim 11 , wherein the patient inhales NO-free air prior to exhaling into the device. 
     
     
       13. A method according to  claim 11 , wherein the patient inhales through the NO-scrubber integrated in said device, supplying NO-free air to the patient, prior to exhaling into the device. 
     
     
       14. A method according to  claim 11 , wherein the patient is given audible or visual feedback during the inhalation and exhalation steps, in order to support the correct performance of said steps. 
     
     
       15. A method according to  claim 11 , wherein the rate at which the sample is fed to the sensor is about 0.5 to 15 ml/s. 
     
     
       16. A method according to  claim 11 , wherein the device comprising an electrochemical NO sensor further comprises a user interface, wherein at least one of the following steps is included:
 the patient enters information relating to his/her intake of a medicament into the user interface; and 
 the patient subjectively assesses his/her state of health and enters corresponding information into the user interface. 
 
     
     
       17. A computer program comprising instructions for performing the method according to  claim 11 , wherein the instructions are stored in a computer-readable medium. 
     
     
       18. A method for diagnostic determination of NO in a gas sample, the method comprising the steps of:
 introducing a sample at a first flow rate into the device of  claim 1 ; 
 storing said sample in the buffer chamber temporarily; 
 feeding said sample to the electrochemical NO sensor at a second flow rate; 
 wherein the first flow rate is higher than the second flow rate. 
 
     
     
       19. The device according to  claim 1 , wherein the flow regulator is configured control the flow rate of the exhalation air to the buffer chamber at a rate of 45-55 ml/s. 
     
     
       20. The device of  claim 1 , further comprising an ambient air inlet connected to the NO scrubber, wherein the ambient air inlet and the combined inlet and outlet are separate structures.